The Pleiades and Triangulum Galaxy

Fall is the time of year when a few deep-sky gems make their way into the night sky once again. The Pleiades, Messier 45, and the Triangulum Galaxy, Messier 33, are on the long list. The Pleiades are also well known to the unaided eye as the Seven Sisters. That is how many stars can only be seen in this open star cluster under dark skies. The image below taken on Insight Observatory's Astronomical Telescope for Educational Outreach (ATEO-1) displays many many more stars in the cluster.

M45 - The Pleiades imaged at LRGB 600 sec, 2x2 bin on ATEO-1 by Insight Observatory. 

The cluster is dominated by hot blue and luminous stars that have formed within the last 100 million years. A faint reflection nebulosity around the brightest stars was thought at first to be leftover from the formation of the cluster (hence the alternative name Maia Nebula after the star Maia), but is now likely an unrelated foreground dust cloud in the interstellar medium, through which the stars are currently passing.

Computer simulations have shown that the Pleiades were probably formed from a compact configuration that resembled the Orion Nebula. Astronomers estimate that the cluster will survive for about another 250 million years, after which it will disperse due to gravitational interactions with its galactic neighborhood.

M33 - The Triangulum Galaxy imaged on ATEO-1 at LRGB 600 sec, 2x2 bin by Insight Observatory.

The Triangulum Galaxy (also known as M33) is about 3 million light-years away from Earth. While its mass is not well understood, one estimate puts it between 10 billion and 40 billion times the sun's mass, what is known is it's the third-largest member of the Local Group or the galaxies that are near the Milky Way. Triangulum also has a small satellite galaxy of its own, called the Pisces Dwarf Galaxy.

Under dark sky conditions, M33 is just barely visible with the naked eye in the constellation Triangulum, just west of Andromeda and Pisces.